In order to fabricate integrated circuits with high device packing densities the semiconductor industry is continually decreasing device dimensions. Reduced device dimensions, however, can also adversely effect device reliability and performance. For example, device parasitics, such as latch-up, hot electron effects, and short channel effects, degrade both the performance and the reliability of semiconductor devices with submicron geometries. These degradation effects, however, can be minimized by fabricating semiconductor devices in silicon-on-insulator (SOI) films. Although SOI films are attractive from a device degradation perspective, current processing techniques often result in the formation of SOI films that have a high crystal defectivity. Semiconductor devices fabricated with these defective SOI films subsequently exhibit poor electrical characteristics, and thus the use of SOI films in the fabrication of high density integrated circuits has been limited.
One method proposed to form a SOI film is solid phase epitaxial re-growth. In this approach, an insulating layer of silicon dioxide is formed over a silicon substrate, and then it is subsequently patterned so that a portion of the silicon substrate is exposed. A layer of amorphous silicon is then deposited over the patterned silicon dioxide layer such that it is in contact with the exposed portion of the silicon substrate. The silicon substrate is subsequently annealed and the amorphous silicon layer is transformed into monocrystalline silicon layer by solid phase epitaxial re-growth. The silicon substrate, which contacts the amorphous silicon layer, acts as epitaxial seed for the re-growth process. The resulting epitaxial film, however, has a high density of crystal defects because the epitaxial re-growth process occurs in a non-uniform manner over the silicon dioxide layer. In addition, silicon dioxide and amorphous silicon have different thermal coefficients of expansion, and thus stress defects are also generated in the epitaxial silicon layer during its formation.
Epitaxial lateral overgrowth (ELO) is another method that has been proposed to form a SOI film. As in the previous technique, a layer of silicon dioxide is formed over a silicon substrate and then an opening is formed through it so that a portion of the silicon substrate is exposed. Silicon is then epitaxially deposited in the opening using the exposed portion of the substrate as an epitaxial seed. The deposition process is continued until the opening is filled and epitaxial silicon has laterally overgrown the patterned silicon dioxide layer. The resulting epitaxial film, however, also has a high density of crystal defects because the epitaxial deposition process is adversely effected by the silicon dioxide layer during the overgrowth process.
Accordingly, a need exists for a low defectivity SOI film that allows high density integrated circuits to be fabricated.